This document specifies requirements and provides guidance for the selection, design, specification, operation, and maintenance of flares and related combustion and mechanical components used in pressure-relieving and vapor-depressurizing systems for petroleum, petrochemical, and natural gas industries. While this document is primarily intended for onshore facilities, guidance related to offshore applications is included. Guidance and best practices for the selection, specification, and mechanical details for flares and on the design, operation, and maintenance of flare combustion and related equipment is also provided. This document is a supplement to API 537, 3rd edition (2017) including the addendum, the requirements of which are applicable with the exceptions specified in this document.